Materials used for protective articles for wear in rain, snow or other wet conditions should keep the wearer dry by preventing the leakage of water into the article and by allowing perspiration to evaporate from the wearer to the outside of the article.
Fabrics treated with silicones, fluorocarbons, and other water repellents usually allow evaporation of perspiration but are only marginally waterproof; they allow water to leak through them under very low pressures, and usually leak spontaneously when rubbed or mechanically flexed.
A recent invention (U.S. Pat. No. 4,194,041) has provided a waterproof and breathable polytetrafluoroethylene (PTFE) laminate that possesses a high moisture vapor transmission rate even under adverse climatic conditions. Such laminates and modified forms thereof are commercially available from W. L. Gore & Associates, Inc. The waterproof and breathable laminate of U.S. Pat. No. 4,194,041 consists of a flexible first layer of a microporous hydrophobic material having a moisture vapor transmission rate exceeding 1000 gms/m.sup.2 day, an advancing water contact angle exceeding 90 degrees and a second layer of continuous hydrophilic elastomeric material attached to the inner face of the first layer whereby the second layer has a moisture vapor transmission rate exceeding 1000 gms/m.sup.2 day and does not permit the detectable passage of liquid water therethrough at hydrostatic pressures of about 24 cm water head and about 172 KN/m.sup.2 for 30 seconds.
The porous membrane of expanded polytetrafluoroethylene (PTFE) used in the above laminate can be provided by following the techniques of U.S. Pat. No. 3,953,566. Such membranes and modified forms thereof are commercially available under the registered trademark GORE-TEX.RTM., sold by W. L. Gore & Associates, Inc. These expanded, porous PTFE membranes satisfy the requirements of being waterproof while also being permeable to the flow of water vapor. The expanded porous PTFE membranes are inherently hydrophobic and contain very small pores that resist the entry of liquid water even at substantial pressures or when rubbed or flexed, but readily allow the flow of gases including water vapor. Unlike wicking materials breathability is achieved by evaporation of liquid water inside the garment or on the inner surface of the membrane followed by gaseous flow or diffusion of water vapor through the membrane to the outside.
In addition to the waterproofness and breathability of protective articles, it is desirable for such articles to have the distinguishing characteristic of stretch. Stretch offers to the consumer many advantages such as comfort, fit, reduced pucker, improved wrinkle resistance, the need for fewer sizes, alterations and greater design flexibility. In its broad concept, "stretch" might be defined as the comfort factor in textile products. In specific textile applications, the technology of stretch relates to fibers, yarns and fabrics; and the extent of its presence in textile products is a matter of its functional advantage for a particular end use.
According to the Encyclopedia of Textiles, third edition, pages 310 to 315, there are two categories of stretch fabrics based on the degree of stretchability. They are: (1) Power or Action Stretch and (2) Comfort Stretch.
"Power Stretch, or Action Stretch, as the names imply, provides a fabric with a high degree of extensibility and quick recovery. The stretch factor generally ranges from at least 30 to 50 percent or more with no more than 5 to 6 percent loss in recovery. Such stretch fabrics are best adapted to skiwear, foundation garments, swimwear, athletic clothing and professional types of active sportwear. Comfort Stretch applies to fabrics with less than a 30 precent stretch factor and no more than 2 to 5 percent loss in recovery. Such fabrics are used in clothing for everyday wear which need only a moderate degree of elasticity."
In the clothing field, increasing use is being made of garments made of stretch fabrics where flexibility of movement is essential; for example, athletic garments, running suits, exercise suits, skiwear, etc. These garments are usually worn where waterproofness and breathability of the garment is desired also.
FIG. 1 shows the percentage of back flex (a), knee flex (b), seat flex(c), and elbow flex (d). The percentage of flex in these areas indicates the minimum degree of stretchability in a fabric needed to maintain comfort to the wearer.
By the addition of strips, inserts or gussets of stretchable material into a nonstretchable waterproof breathable garment, partial stretch and flexibility is imparted to the garment. In addition, it is desirable to use stretch fabrics for the collars, cuffs and waistbands of stretch garments and other garments, as well. However, waterproofness and breathability of these strips, inserts, or gussets is desired also in order to make the garments totally waterproof and breathable while introducing partial stretch and flexibility to the garments.